Photovoltaic cells produce DC power over a wide voltage range depending on the amount of sunlight, ambient temperature and wind speed. A minimum DC voltage is required to directly convert this DC voltage to a standard 120 Volts AC and to do so without the use of a 60 cycle transformer. There are National Electric Code restrictions and class-of-equipment considerations that make photovoltaic arrays much more cost effective when sized for a maximum of 600 Vdc. The problem is that under some conditions, photovoltaic arrays sized for this 600 Vdc maximum will not meet the said minimum voltage requirements for direct DC to AC conversion. The prior art inverters would either use a 60 cycle transformer, a dual boost converter input stage or a full-bridge input stage with a high frequency transformer to achieve the proper voltage match over the predicted range of inverter operation. A 60 cycle transformer decreases power conversion efficiency and adds to the overall inverter or system costs. A dual boost converter input stage or a full-bridge input stage adds complexity to and lowers the conversion efficiency of the inverter.
The, prior art, dual boost converter and full directly or indirectly, is old technology and is well known. The single-switch bipolar boost converter, disclosed herein, is a novel replacement for the dual boost converter. The single-switch bipolar boost converter is less complex, lower cost and provides higher power conversion efficiencies.